EP-A-370 890 in the name of Technomed Medical Systems, S.A. ("the '890 Publication") discloses a microwave therapy probe for treatment of the prostate. The probe includes means for cooling the urethral wall of the prostate during treatment. The probe disclosed in this publication also includes temperature measuring sensors. More specifically, the probe includes a fibre-optic temperature sensor to measure the temperature at the surface of the urethral probe, and an interstitial probe to measure the temperature inside of the prostate. The '890 Publication suggests controlling the power delivered to the probe by a microwave generator according to the temperature measured by the temperature sensors, and according to the temperature of the coolant. No further explanation as to temperature control is given in this publication. There is nothing in this publication suggesting to the person of ordinary skill in the art that the temperature of the coolant could vary.
The transurethral microwave apparatus sold by Technomed Medical Systems under the trademark PROSTATRON uses a rectal probe for monitoring treatment and an urethral probe containing the microwave antenna. Four temperature sensors are present in the apparatus: one sensor is located in the urethral probe and the other three sensors are located on the surface of a specially designed rectal probe, which sensors face the prostate. A description of this probe is given in FR-A-2 660 561.The urethral probe utilizes a coolant to cool the surface of the probe facing the urethral wall. In this apparatus, the microwave power and the temperature of the coolant are computer controlled. The coolant is kept at a constant temperature of about 20.degree. C. Microwave power gradually increases up to about 60 W or 70 W during the first 20 minutes of the treatment. The power is then held constant unless a preset maximum temperature is measured by one of the sensors. In that case, the microwave emission is stopped to permit cooling of the rectum or the urethra and thereby prevent overheating. This technique prevents overheating the rectum wall or burning of the urethra. When the temperatures drop to below a threshold, microwave emission is resumed. This apparatus permits a shorter treatment duration, typically one session of less than one hour, and provides proper and efficient treatment of the patient.
U.S. Pat. No. 5,509,929 assigned to Technomed Medical Systems, S.A. discloses a microwave urethral probe with an inflatable balloon for anchoring the probe in the bladder of a patient. The primary active heating part of the microwave antenna is arranged to direct microwave energy on the prostatic tissues located near the bladder neck when the probe is in an operational position.
U.S. Pat. No. 5,843,144 assigned to Urologix Inc. discloses a method for treating benign prostatic hyperplasia with microwave thermal therapy. The probe described in this patent has a microwave antenna, an inflatable balloon for anchoring the probe in the bladder of the patient, and coolant duct for cooling the urethral wall near the prostate. The main heating part of the antenna is located below the bladder neck, substantially in the center of the prostate. This patent suggests minimizing the number of interruptions of microwave power applied to prostatic tissues. To achieve this result, the patent suggests applying prechilling to the urethral wall before beginning microwave treatment. The coolant is then maintained at a constant temperature during the treatment phase. After the end of the treatment, the coolant is maintained at a low temperature to reduce edema. The total duration of the treatment according to this patent is around 88 minutes, 67 minutes of which correspond to the microwave generating phases, i.e., microwave power ramping up for about 17 minutes and continuous heating of tissues for about 50 minutes. To control microwave power during the continuous heating of tissues, this patent suggests monitoring the rectal temperature and the probe temperature, and increasing or decreasing power to maintain the temperature of the rectum below 42.degree. C. and maintain the probe temperature within 1.degree. C. of 40.degree. C. There is no provision for automatically adjusting the power to meet these temperature targets.